Apparatus and method for supplying hybrid power in marine plant

ABSTRACT

The present invention relates to an apparatus and method for supplying hybrid power using a regenerative power generated in a marine plant. An embodiment of the present invention provides a hybrid power supply apparatus in a marine plant, the hybrid power supply apparatus comprising: a generator; an AC/DC converter which converts an alternating current produced by the generator into a direct current and supplies the direct current to a DC bus; a power load which is connected to the DC bus and generates a regenerative power; a first DC/DC converter which is connected to the DC bus; a first power storage unit which is connected to the first DC/DC converter and stores power; and a first resistor unit which is connected to the first DC/DC converter and consumes power when the first power storage unit&#39;s capacity is full.

TECHNICAL FIELD

The present invention relates to hybrid power supply for an offshoreplant, and, more particularly, to a hybrid power supply apparatus andmethod using regenerative power generated in an offshore plant.

BACKGROUND ART

With rapid industrialization and industrial development, consumption ofresources such as petroleum has increased, and stable production andsupply of oil have become a crucial global problem.

For this reason, development of smaller marginal fields or deep-sea oilfields, which has been ignored due to lack of economic feasibility, isnow emerging. Thus, development of offshore plants provided with oildrilling equipment suitable for use in such oil fields is activelycarried out along with development of seabed mining technology.

An offshore plant is provided with various types of drilling-relatedequipment such as a Derrick crane system, a draw-works, a top drive, amud pump, a cement pump, a riser, and a drill pipe.

The draw-works performs lifting of the drill pipe, insertion of acasing, and the like, and includes a drum and a motor. The drum ispowered by the motor so as to wind or unwind a wire rope for controllinglifting of the drill pipe. The rotational speed of the motor can beadjusted so as to adjust the rotational speed of the drum, therebyenabling adjustment of the speed of the drill pipe.

The top drive provides power for drilling and pipe fastening in drillingoperation.

Offshore plants are divided into a stationary platform anchored at onepoint of nearshore to perform drilling operations and a floatingoffshore plant capable of performing drilling operation at ocean depthsof 3,000 m or more.

The floating offshore plant is provided with a plurality of thrusters asa main propulsion device or a propulsion device for computer-aideddynamic positioning. The thrusters are located at the bottom of a shipto change an operating direction of a propeller and are commonly used toallow the ship to navigate or to sail in a canal or enter/leave a portunder its own power without a tug. The thruster is powered by a thrustmotor connected thereto.

FIG. 1 is a diagram of a typical power supply system known in the art.

Referring to FIG. 1, AC power generated by a power generator 110 issupplied to an AC bus, to which a first AC/DC converter 121, a secondAC/DC converter 122, and a third AC/DC converter 123 are connected.

The first AC/DC converter 121 converts alternating current supplied fromthe AC bus into direct current and supplies the direct current to afirst DC bus 131, and a DC/AC converter 141 converts direct currentsupplied from the first DC bus 131 into alternating current and suppliesthe alternating current to a first thruster motor 151.

The second AC/DC converter 122 converts alternating current suppliedfrom the AC bus into direct current and supplies the direct current to asecond DC bus 132, and a DC/AC converter 142 converts direct currentsupplied from the second DC bus 132 into alternating current andsupplies the alternating current to a second thruster motor 152.

The third AC/DC converter 123 converts alternating current supplied fromthe AC bus into direct current and supplies the direct current to athird DC bus 133, and a plurality of DC/AC converters 143 to 148 areconnected to the third DC bus 133. The plurality of DC/AC converters 143to 148 convert direct current supplied from the third DC bus 133 intoalternating current and supply the alternating current to correspondingones of a plurality of draw-works motors 153, 154, 155, 158, 159 and aplurality of top drive motors 156, 157.

Since the draw-works motors 153, 154, 155, 158, 159 and the top drivemotors 156, 157 are configured to repeatedly lift or lower drillingequipment such as a drill pipe, a brake is frequently put on the motorsto bring the motors to a sudden stop or to rotate the motors in areverse direction during rotation at rated load, and, for the thrustermotors 151, 152, a brake is also frequently put on the motors to bringthe motors to a sudden stop or to rotate the motors in the reversedirection during rotation at rated load. When a brake is put on themotors, regenerative power is generated in the motors. In addition, whena thruster is rotated due to a disturbance, regenerative power is alsogenerated in the thruster motors.

When regenerative power is generated in the draw-works motors, the topdrive motors, or the thruster motors, voltage of a DC bus connected tothe draw-works motors, the top drive motors, or the thruster motors isincreased, and, when the voltage is increased beyond a degree which theDC bus can accommodate, the DC bus is tripped.

Thus, the typical power supply system is provided with resistors 161 to166 to consume regenerative power as heat, thereby preventing the DC busfrom tripping.

FIG. 2 is a graph showing power consumption of each component of atypical power supply system known in the art.

Referring to FIG. 2, electric power produced by a power generator issupplied to a first load 220 and an AC/DC converter 260 through adistributor. The AC/DC converter 260 converts alternating current intodirect current and supplies the direct current to a second load 240while supplying the direct current to a draw-works 230 through a DC/ACconverter. Each of the first load 220 and the second load 240 is a loadthat consumes a constant level of electric power. On the contrary, powerconsumption of the draw-works 230 changes continuously, and, in FIG. 2,a negative value of electric power means that regenerative power isgenerated. Regenerative power generated in the draw-works 230 isconsumed by the second load or a resistor 250.

In FIG. 2, it can be seen that abrupt change in power consumption of thedraw-works 230 causes abrupt change in power output of the powergenerator 210. A diesel power generator consumes more fuel anddischarges more exhaust gas in the case where power output is abruptlychanged than in the case where power output is maintained at a constantlevel.

In order to supply suitable electric power corresponding to abruptchange in power consumption of the draw-works motors, the top drivemotors, and the thruster motors, it is necessary to rapidly change poweroutput of the power generator. However, the power generator hasdifficulty providing suitable electric power corresponding to abruptchange in power consumption of the draw-works motors, the top drivemotors, and the thruster motors due to low responsiveness thereof. Ifsuitable power supply to the draw-works motors, the top drive motors,and the thruster motors is not achieved, a dangerous situation can occurdue to characteristics of drilling operation. Further, when power supplyto the draw-works motors or the top drive motors is suddenly interruptedupon loss of power, a dangerous situation can also occur.

In other words, typical power supply systems have problems such asenergy waste due to consumption of regenerative power by resistors,increase in fuel consumption and exhaust gas due to abrupt change inpower output of a power generator, difficulty in suitable electric powersupply to draw-works motors, top drive motors, and thruster motors, anddanger upon loss of power.

DISCLOSURE Technical Problem

It is an aspect of the present invention to provide a hybrid powersupply apparatus and method for an offshore plant which can efficientlyutilize regenerative power, maintain power output of a generator at aconstant level, supply suitable electric power corresponding to abruptchange in power consumption of electric loads, and supply electric powerupon sudden loss of power.

Technical Solution

In accordance with one aspect of the present invention, there isprovided a hybrid power supply apparatus for an offshore plant,including: a power generator; an AC/DC converter converting alternatingcurrent produced by the power generator into direct current andsupplying the direct current to a DC bus; an electric power loadconnected to the DC bus and generating regenerative power; a first DC/DCconverter connected to the DC bus; a first power storage unit connectedto the first DC/DC converter and storing electric power; and a firstresistor connected to the first DC/DC converter and consuming electricpower when the first power storage unit is full.

The first DC/DC converter may measure voltage of the DC bus, and mayallow the first power storage unit to store electric power when thevoltage of the DC bus is maintained at a first threshold value or higherfor a first period of time.

The first DC/DC converter may measure the voltage of the DC bus, and mayallow the first resistor to consume electric power when the voltage ofthe DC bus is maintained at the first threshold value or higher for asecond period of time, and wherein the second period of time is longerthan the first period of time.

The hybrid power supply apparatus may further include: a second powerstorage unit and a second resistor.

The DC bus may be connected to a second DC/DC converter, and the secondpower storage unit and the second resistor may be connected to thesecond DC/DC converter.

The first power storage unit may be an ultracapacitor.

The electric power load may be a draw-works.

The electric power load may be a top drive.

In accordance with another aspect of the present invention, there isprovided a hybrid power supply method for an offshore plant, including:measuring, by a DC/DC converter, voltage of a DC bus; storing, by apower storage unit, electric power when the voltage of the DC bus ismaintained at a first threshold value or higher for a first period oftime; and consuming, by a resistor, electric power when the voltage ofthe DC bus is maintained at the first threshold value or higher for asecond period of time, wherein the DC bus is connected to an electricpower load generating regenerative power and the second period of timeis longer than the first period of time.

The DC/DC converter may measure the voltage of the DC bus, and may allowelectric power to flow from the DC bus to the power storage unit suchthat the power storage unit stores electric power, when the voltage ofthe DC bus is maintained at the first threshold value or higher for thefirst period of time.

The DC/DC converter may measure the voltage of the DC bus, and may allowelectric power to flow from the DC bus to the resistor such that theresistor consumes electric power when the voltage of the DC bus ismaintained at the first threshold value or higher for the second periodof time.

The power storage unit may be an ultracapacitor.

The electric power load may be a draw-works.

The electric power load may be a top drive.

In accordance with a further aspect of the present invention, there isprovided a hybrid power supply apparatus for an offshore plant,including: a power generator; an AC/DC converter converting alternatingcurrent produced by the power generator into direct current andsupplying the direct current to a DC bus; a first electric power loadconnected to the DC bus via a first DC/AC converter and generatingregenerative power; a first power storage unit storing regenerativepower when regenerative power is generated in the first electric powerload; a first resistor consuming electric power when the first powerstorage unit is full; a second electric power load connected to the DCbus via a second DC/AC converter and generating regenerative power; asecond power storage unit storing regenerative power when regenerativepower is generated in the second electric power load; and a secondresistor consuming electric power when the second power storage unit isfull.

The hybrid power supply apparatus may further include: a first DC/DCconverter connected to the DC bus; and a second DC/DC converterconnected to the DC bus, wherein the first power storage unit and thefirst resistor are connected to the first DC/DC converter, and thesecond power storage unit and the second resistor are connected to thesecond DC/DC converter.

The first DC/AC converter may detect whether regenerative power isgenerated in the first electric power load, and send a control signal tothe first DC/DC converter when regenerative power is generated in thefirst electric power load, and the first DC/DC converter may allowelectric power to be supplied from the DC bus to the first power storageunit in response to the control signal such that the first power storageunit stores electric power.

The first DC/DC converter may allow electric power to be supplied fromthe DC bus to the first resistor such that the first resistor consumeselectric power when detecting that the first power storage unit is full.

The first power storage unit may be an ultracapacitor.

The first electric power load may be a draw-works.

The first electric power load may be a top drive.

The hybrid power supply apparatus may further include: a first DC/DCconverter connected to the DC bus; a second DC/DC converter connected tothe DC bus; a third DC/DC converter connected to the DC bus; and afourth DC/DC converter connected to the DC bus, wherein the first powerstorage unit may be connected to the first DC/DC converter, the firstresistor may be connected to the second DC/DC converter, the secondpower storage unit may be connected to the third DC/DC converter, andthe second resistor may be connected to the fourth DC/DC converter.

In accordance with yet another aspect of the present invention, there isprovided a hybrid power supply method for an offshore plant, including:detecting, by a first DC/AC converter, whether regenerative power isgenerated in a first electric power load; storing, by a first powerstorage unit, regenerative power generated in the first electric powerload; detecting, by a second DC/AC converter, whether regenerative poweris generated in a second electric power load; and storing, by a secondpower storage unit, regenerative power generated in the second electricpower load, wherein the first DC/AC converter and the second DC/ACconverter may be connected to a DC bus, the first electric power loadmay be connected to the first DC/AC converter, and the second electricpower load may be connected to the second DC/AC converter.

The DC bus may be connected to a first DC/DC converter and a secondDC/DC converter; the first power storage unit and a first resistor maybe connected to the first DC/DC converter; and the second power storageunit and a second resistor may be connected to the second DC/DCconverter.

The hybrid power supply method may further include: sending, by thefirst DC/AC converter, a control signal indicative of generation ofregenerative power in the first electric power load to the first DC/DCconverter; and allowing, by the first DC/DC converter, electric power tobe supplied from the DC bus to the first power storage unit in responseto the control signal such that the first power storage unit storeselectric power.

The hybrid power supply method may further include: detecting, the firstDC/DC converter, that the first power storage unit is full; andallowing, by the first DC/DC converter, electric power to be suppliedfrom the DC bus to the first resistor such that the first resistorconsumes.

The hybrid power supply method may further include: consuming, by thesecond resistor, electric power when the second power storage unit isfull.

The first power storage unit may be an ultracapacitor.

The first electric power load may be a draw-works.

The first electric power load may be a top drive.

Advantageous Effects

According to embodiments of the present invention, it is possible toprovide a hybrid power supply apparatus and method which allowregenerative power generated in a draw-works motor, a top drive motor,and a thruster motor to be stored in a power storage unit and supplyelectric power stored in the power storage unit upon abrupt increase inpower consumption of the draw-works motor, the top drive motor, and thethruster motor to efficiently utilize regenerative power whilemaintaining power output of a power generator at a constant level toreduce exhaust gas.

In addition, it is possible to provide a hybrid power supply apparatusand method which use an ultracapacitor having high responsiveness as apower storage unit, thereby supplying suitable electric powercorresponding to abrupt change in power consumption of electric loads.

Further, it is possible to provide a hybrid power supply apparatus andmethod which can utilize electric power stored in a power storage unitto safely shut down drilling equipment such as a draw-works or a topdrive upon transients or loss of power.

Furthermore, it is possible to provide a hybrid power supply apparatusand method which can reduce the number of DC/DC converters by connectinga power storage unit and a resistor to a single DC/DC converter, therebyreducing equipment size and costs.

Furthermore, it is possible to provide a hybrid power supply apparatusand method which can operate a set of an electric power load, a powerstorage unit, and a resistor in an individual manner by allocating adedicated power storage unit and a dedicated resistor to a specificelectric power load.

DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram of a typical power supply system known in the art.

FIG. 2 is a graph showing power consumption of each component of atypical power supply system known in the art.

FIG. 3 is a diagram of a hybrid power supply apparatus for an offshoreplant according to a first embodiment of the present invention.

FIG. 4 is a diagram of a hybrid power supply apparatus for an offshoreplant according to a second embodiment of the present invention.

FIG. 5 is a diagram of a hybrid power supply apparatus for an offshoreplant according to a third embodiment of the present invention.

FIG. 6 is a flowchart of a process of supplying electric power to apower storage unit in a hybrid power supply method for an offshore plantaccording to an embodiment of the present invention.

FIG. 7 is a flowchart of a process of supplying electric power from thepower storage unit to a DC bus upon power shortage in the hybrid powersupply method for an offshore plant according to the embodiment of thepresent invention.

FIG. 8 is a flowchart of a process of supplying electric power from thepower storage unit to the DC bus upon loss of power in the hybrid powersupply method for an offshore plant according to the embodiment of thepresent invention.

FIG. 9 is a graph showing power consumption of each component of thepower supply apparatus according to the embodiments of the presentinvention.

EMBODIMENTS

Hereinafter, embodiments of the present invention will be described withreference to the accompanying drawings. It should be noted that likecomponents will be denoted by like reference numerals throughout thespecification and the accompanying drawings. In addition, descriptionsof details apparent to those skilled in the art will be omitted forclarity.

First, a hybrid power supply apparatus for an offshore plant accordingto embodiments of the present invention will be described with referenceto FIGS. 3 to 5. FIG. 3 is a diagram of a hybrid power supply apparatusfor an offshore plant according to a first embodiment of the presentinvention, FIG. 4 is a diagram of a hybrid power supply apparatus for anoffshore plant according to a second embodiment of the presentinvention, and FIG. 5 is a diagram of a hybrid power supply apparatusfor an offshore plant according to a third embodiment of the presentinvention.

Referring to FIGS. 3 to 5, a hybrid power supply apparatus for anoffshore plant according to the first embodiment of the presentinvention includes a power generator 310, an AC/DC converter 320, a DCbus 321, a variable frequency drive (VFD) controller 330, DC/DCconverters 351 to 353, electric power loads 361 to 363, power storageunits 371 to 373, resistors 381 to 383, and a sensor 391.

The power generator 310 is a device producing electric power for anoffshore plant and is connected to the AC/DC converter 320 via an ACbus. Alternatively, electric power produced by the power generator 310may be supplied to the AC/DC converter 320 after being altered to avoltage suitable for use in electric power loads. The power generator310 is an AC Generator and can produce AC power.

The AC/DC converter 320 converts AC power produced by the powergenerator 310 into direct current and supplies the direct current to theDC bus 321.

The DC bus 321 supplies electric power to electric power loads connectedto the DC bus 321. Electric power loads using DC power may be connecteddirectly to the DC bus 321, and electric power loads using AC power maybe connected to the DC bus 321 via DC/AC converters (341 to 343).

The electric power loads 361 to 363 of FIG. 3 are electric power loadsusing AC power and are connected to the DC bus 321 via the DC/ACconverters 341 to 343, respectively. The DC/AC converters 341 to 343convert direct current supplied from the DC bus 321 into alternatingcurrent and supply the alternating current to the electric power loads361 to 363, respectively.

The electric power loads 361 to 363 may be draw-works motors or topdrive motors.

Although, in FIG. 3, three draw-works motors 361 to 363, as the electricpower loads, are shown as being connected to the DC bus 321, it shouldbe understood that the present invention is not limited thereto and avarying number of draw-works motors and top drive motors may beconnected to the DC bus 321.

Since the draw-works motors 361 to 363 are configured to repeatedly liftor lower drilling equipment such as a drill pipe, a brake is frequentlyput on the motors to bring the motors to a sudden stop or to rotate themotors in a reverse direction during rotation at rated load.

The power storage units 371 to 373 receive electric power from the DCbus 321 so as to store the electric power when a voltage of the DC bus321 is maintained at a first threshold value or higher for a firstperiod of time, and the power storage units supply electric power to theDC bus 321 when the voltage of the DC bus 321 is maintained at a secondthreshold value or less for a second period of time. For example,assuming that the DC bus 321 is a 720 V DC bus and is tripped at 750 Vor higher, the first threshold value may be set to 740 V.

The DC/DC converters 351 to 353 measure the voltage of the DC bus 321,and supply electric power from the DC bus 321 to the power storage units371 to 373 such that the power storage units 371 to 373 store electricpower when the voltage of the DC bus is maintained at the firstthreshold value or higher for the first period of time, whereas theDC/DC converters allow electric power to flow from the power storageunits 371 to 373 to the DC bus 321 to supply electric power from thepower storage units 371 to 373 to the DC bus 321 when the voltage of theDC bus is maintained at the second threshold value or less for thesecond period of time.

When regenerative power is generated in the electric power loads 361 to363, the voltage of the DC bus 321 is increased, and, when powerconsumption of the electric power loads 361 to 363 is abruptlyincreased, the voltage of the DC bus 321 drops.

In other words, when regenerative power is generated in the electricpower loads 361 to 363 causing increase in the voltage of the DC bus 321and the voltage of the DC bus 321 is maintained at the threshold valueor higher for the first period of time, the DC/DC converters 351 to 353supply electric power to the power storage units 371 to 373 such thatthe power storage units 371 to 373 store electric power, therebyallowing regenerative power generated in the electric power loads 361 to363 to be stored in the power storage units 371 to 373.

When power consumption of the electric power loads 361 to 363 isabruptly increased causing drop in the voltage of the DC bus 321 and thevoltage of the DC bus 321 is maintained at the second threshold value orless for the second period of time, the DC/DC converters 351 to 353allow electric power to flow from the power storage units 371 to 373 tothe DC bus 321 such that the DC bus 321 receives electric power from thepower storage units 371 to 373. The power storage units 371 to 373 maybe at least of an ultracapacitor, a capacitor, a battery, and aflywheel. Particularly, when the power storage units 371 to 373 areultracapacitors, it is possible to rapidly supply electric power to theelectric power loads 361 to 363 upon a sudden increase in powerconsumption of the electric power loads 361 to 363 since such anultracapacitor has higher responsiveness than the power generator 310.

In addition, the power storage units 371 to 373 can supply electricpower to the DC bus 321 upon transients or loss of power. When a sensorfor detecting transients or loss of power 391 senses a transient or lossof power and sends detection signals to the DC/DC converters 351 to 353,the DC/DC converters 351 to 353 allow electric power to be supplied fromthe power storage units 371 to 373 to the DC bus 321.

The sensor 391 may be mounted on at least one of a switchboard and theDC bus 321.

Drilling equipment such as a draw-works and a top drive can cause adangerous situation upon abrupt interruption of power supply. Thus, thepower storage units 371 to 373 supply electric power to the DC bus 321upon transients or loss of power to safely shut down the drillingequipment.

The resistors 381 to 383 consume electric power when the voltage of theDC bus 321 is maintained at the first threshold value or higher for athird period of time. Here, the third period of time is longer than thefirst period of time.

When regenerative power is generated in the electric power loads 361 to363 causing increase in the voltage of the DC bus 321 and the voltage ofthe DC bus is maintained at the threshold value or higher for the firstperiod of time, the power storage units 371 to 373 store electric power.When the power storage units 371 to 373 are full, the voltage of the DCbus 321 does not drop and is continuously maintained at the firstthreshold value or higher. Thus, if the voltage of the DC bus 321 ismaintained at the first threshold value or higher for the third periodof time, it can be determined that the power storage units 371 to 373are full. When regenerative power is continuously generated even afterthe power storage units 371 to 373 are full, the voltage of the DC bus321 continuously increases, thereby causing the DC bus 321 to betripped. Thus, when the voltage of the DC bus 321 is maintained at thefirst threshold value or higher for the third period of time, the DC/DCconverters 351 to 353 allow the resistors 381 to 383 to consume electricpower.

Although FIGS. 3 to 5 show three power storage units 371 to 373 andthree resistors 381 to 383, it should be understood that the presentinvention is not limited thereto and may include varying numbers ofpower storage units and resistors.

As shown in FIG. 3, the power storage units 371 to 373 and thecorresponding resistors 381 to 383 may be connected to the DC bus 321 inpairs. In other words, a first power storage unit 371 and a firstresistor 381 are connected to the DC bus 321 via a first DC/DC converter351; a second power storage unit 372 and a second resistor 382 areconnected to the DC bus 321 via a second DC/DC converter 352; and athird power storage unit 373 and a third resistor 383 are connected tothe DC bus 321 via a third DC/DC converter 353. When the power storageunit and the resistor are connected to the same DC/DC converter, as inFIG. 3, it is possible to reduce the number of required DC/DC convertersand the overall size of the apparatus.

Alternatively, the plural power storage units 371 to 373 and the pluralresistors 381 to 383 may be connected to the DC bus 321 via separateDC/DC converters 451 to 456, respectively, as shown in FIG. 4. In otherwords, a first power storage unit 371 is connected to the DC bus 321 viaa first DC/DC converter 451; a second power storage unit 372 isconnected to the DC bus 321 via a second DC/DC converter 452; a thirdpower storage unit 373 is connected to the DC bus 321 via a third DC/DCconverter 453; a first resistor 381 is connected to the DC bus 321 via afourth DC/DC converter 454; a second resistor 382 is connected to the DCbus 321 via a fifth DC/DC converter 455; and a third resistor 383 isconnected to the DC bus 321 via a sixth DC/DC converter 456. When theplural power storage units 371 to 373 and the plural resistors 381 to383 are connected to separate DC/DC converters 451 to 456, respectively,as in FIG. 4, it is possible to operate the plural power storage units371 to 373 and the plural resistors 381 to 383 in an individual manner.

Alternatively, a single power storage unit 371 to 373 and a singleresistor 381 to 383 may be dedicated to a single electric power load 361to 363, as shown in FIG. 5. In other words, when regenerative power isgenerated in a first electric power load 361, a first power storage unit371 stores the regenerative power and a first resistor 381 does notconsume electric power until the first power storage unit 371 is full.When regenerative power is generated in a second electric power load362, a second power storage unit 372 stores the regenerative power and asecond resistor 382 does not consume electric power until the secondpower storage unit 372 is full. When regenerative power is generated ina third electric power load 363, a third power storage unit 373 storesthe regenerative power and a third resistor 383 does not consumeelectric power until the third power storage unit 372 is full.

When regenerative power is generated in the first electric power load361, a first DC/AC converter 341 detects generation of regenerativepower in the first electric power load 361 and sends a control signal tothe first DC/DC converter 351. In response to the control signal, thefirst DC/DC converter 351 allows electric power to be supplied from theDC bus 321 to the first power storage unit 371 such that the first powerstorage unit 371 can store electric power. Then, the first DC/DCconverter 351 detects whether the first power storage unit 371 is full,and, when the first power storage unit 371 is full, the first DC/DCconverter allows the first resistor 381 to consume electric power.Although the first power storage unit 371 and the first resistor 381 areshown as being connected to the same DC/DC converter 351, it should beunderstood that the first power storage unit 371 and the first resistor381 may be connected to different DC/DC converters.

Next, a hybrid power supply method for an offshore plant according to anembodiment of the present invention will be described with reference toFIGS. 6 to 8. FIG. 6 is a flowchart of a process of supplying electricpower to a power storage unit in a hybrid power supply method for anoffshore plant according to an embodiment of the present invention, FIG.7 is a flowchart of a process of supplying electric power from the powerstorage unit to a DC bus upon power shortage in the hybrid power supplymethod for an offshore plant according to the embodiment of the presentinvention, and FIG. 8 is a flowchart of a process of supplying electricpower from the power storage unit to the DC bus upon loss of power inthe hybrid power supply method for an offshore plant according to theembodiment of the invention.

Referring to FIG. 6, voltage of a DC bus is measured (S610); electricpower is stored in a power storage unit when the voltage of the DC bus321 is maintained at a first threshold value or higher for a firstperiod of time (S620); and electric power is consumed by a resistor whenthe voltage of the DC bus 321 is maintained at the first threshold valueor higher for a second period of time (S630).

Referring to FIG. 7, the voltage of the DC bus is measured (S710); andelectric power stored in the power storage unit is supplied to the DCbus when the voltage of the DC bus is maintained at a second thresholdvalue or less for a third period of time (S720).

When a sensor 391 detects loss of power (S810), the sensor 391 sends acontrol signal to a DC/DC converter (S820), and the DC/DC converterallows the power storage unit to supply electric power to the DC bus inresponse to the control signal from the sensor 391 (S830).

Next, power consumption of each component of the power supply apparatusaccording to the embodiments of the invention will be described withreference to FIG. 9. FIG. 9 is a graph showing power consumption of eachcomponent of the power supply apparatus according to the embodiments ofthe invention.

As shown in FIG. 9, it can be seen that, when regenerative power isgenerated in the electric power load, the power storage unit stores thegenerated regenerative power, and, when power consumption of theelectric power load is suddenly increased, the power storage unitsupplies electric power to the electric power load, thereby maintainingpower output of the power generator at a constant level.

Although some embodiments have been described herein, it should beunderstood by those skilled in the art that these embodiments are givenby way of illustration only, and that various modifications, variationsand alterations can be made without departing from the spirit and scopeof the invention. Therefore, the embodiments disclosed herein should notbe construed as limiting the technical scope of the present invention,but should be construed as illustrating the idea of the presentinvention. The scope of the present invention should be interpretedaccording to the appended claims as covering all modifications orvariations derived from the appended claims and equivalents thereof.

1. A hybrid power supply apparatus for an offshore plant, comprising: apower generator; an AC/DC converter converting alternating currentproduced by the power generator into direct current and supplying thedirect current to a DC bus; an electric power load connected to the DCbus and generating regenerative power; a first DC/DC converter connectedto the DC bus; a first power storage unit connected to the first DC/DCconverter and storing electric power; and a first resistor connected tothe first DC/DC converter and consuming electric power when the firstpower storage unit is full.
 2. The hybrid power supply apparatusaccording to claim 1, wherein the first DC/DC converter measures voltageof the DC bus, and allows the first power storage unit to store electricpower when the voltage of the DC bus is maintained at a first thresholdvalue or higher for a first period of time.
 3. The hybrid power supplyapparatus according to claim 2, wherein the first DC/DC convertermeasures the voltage of the DC bus, and allows the first resistor toconsume electric power when the voltage of the DC bus is maintained atthe first threshold value or higher for a second period of time, andwherein the second period of time is longer than the first period oftime.
 4. The hybrid power supply apparatus according to claim 2, furthercomprising: a second power storage unit and a second resistor.
 5. Thehybrid power supply apparatus according to claim 4, wherein the DC busis connected to a second DC/DC converter, and the second power storageunit and the second resistor are connected to the second DC/DCconverter.
 6. The hybrid power supply apparatus according to claim 1,wherein the first power storage unit is an ultracapacitor.
 7. The hybridpower supply apparatus according to claim 1, wherein the electric powerload is a draw-works.
 8. The hybrid power supply apparatus according toclaim 1, wherein the electric power load is a top drive.
 9. A hybridpower supply method for an offshore plant, comprising: measuring, by aDC/DC converter, voltage of a DC bus; storing, by a first power storageunit, electric power when the voltage of the DC bus is maintained at afirst threshold value or higher for a first period of time; andconsuming, by a resistor, electric power when the voltage of the DC busis maintained at the first threshold value or higher for a second periodof time, wherein the DC bus is connected to a first electric power loadgenerating regenerative power and the second period of time is longerthan the first period of time.
 10. The hybrid power supply methodaccording to claim 9, wherein the DC/DC converter measures the voltageof the DC bus, and allows electric power to flow from the DC bus to thefirst power storage unit such that the first power storage unit storeselectric power, when the voltage of the DC bus is maintained at thefirst threshold value or higher for the first period of time.
 11. Thehybrid power supply method according to claim 10, wherein the DC/DCconverter measures the voltage of the DC bus, and allows electric powerto flow from the DC bus to the resistor such that the resistor consumeselectric power when the voltage of the DC bus is maintained at the firstthreshold value or higher for the second period of time. 12-16.(canceled)
 17. The hybrid power supply apparatus according to claim 1,further comprising a first DC/AC converter connecting the electric powerload with the DC bus, wherein the first DC/AC converter detects whetherregenerative power is generated in the electric power load, and sends acontrol signal to the first DC/DC converter when regenerative power isgenerated in the electric power load, and the first DC/DC converterallows electric power to be supplied from the DC bus to the first powerstorage unit in response to the control signal such that the first powerstorage unit stores electric power.
 18. The hybrid power supplyapparatus according to claim 17, wherein the first DC/DC converterallows electric power to be supplied from the DC bus to the firstresistor such that the first resistor consumes electric power whendetecting that the first power storage unit is full. 19-22. (canceled)23. The hybrid power supply method according to claim 9, furthercomprising: detecting, by a first DC/AC converter, whether regenerativepower is generated in the first electric power load; storing, by thefirst power storage unit, regenerative power generated in the firstelectric power load; detecting, by a second DC/AC converter, whetherregenerative power is generated in a second electric power load; andstoring, by a second power storage unit, regenerative power generated inthe second electric power load; wherein the first DC/AC converter andthe second DC/AC converter are connected to a DC bus, the first electricpower load is connected to the first DC/AC converter, and the secondelectric power load is connected to the second DC/AC converter. 24-30.(canceled)